package com.wc.alorithm_blue_bridge._思维.blue密钥;

import java.io.BufferedReader;
import java.io.IOException;
import java.io.InputStreamReader;
import java.io.PrintWriter;
import java.util.StringTokenizer;

/**
 * @Author congge
 * @Date 2025/6/7 19:26
 * @description
 * https://www.lanqiao.cn/problems/20324/learning/?contest_id=256
 */
public class Main {
    static FastReader sc = new FastReader();
    static PrintWriter out = new PrintWriter(System.out);
    static int N = 200010;
    static char[] s;
    static int[][] f = new int[5][5];
    static char[] t = "blue".toCharArray();
    static int n;

    public static void main(String[] args) {
        s = sc.next().toCharArray();
        n = s.length;
        for (int j = 0; j <= 3; j++) {
            for (int k = 0; k <= 3; k++) {
                for (int i = k; i < n; i += 4) {
                    if (s[i] == t[(j + k) % 4]) f[j][k]++;
                }
            }
        }
        int res = 0;
        for (int i = 0; i <= 3; i++) {
            int row = n;
            for (int j = 0; j <= 3; j++) {
                row = Math.min(row, f[i][j]);
            }
            // 只有接近 n / 4 的时候，我们可以变一个出来
            if (row + res == n / 4 && row > 0 && i > 0) row--;
            res += row;
        }
        out.println(res);
        out.flush();
    }
}

class FastReader {
    StringTokenizer st;
    BufferedReader br;

    FastReader() {
        br = new BufferedReader(new InputStreamReader(System.in));
    }

    String next() {
        while (st == null || !st.hasMoreElements()) {
            try {
                st = new StringTokenizer(br.readLine());
            } catch (IOException e) {
                e.printStackTrace();
            }
        }
        return st.nextToken();
    }

    int nextInt() {
        return Integer.parseInt(next());
    }

    String nextLine() {
        String s = "";
        try {
            s = br.readLine();
        } catch (IOException e) {
            e.printStackTrace();
        }
        return s;
    }

    long nextLong() {
        return Long.parseLong(next());
    }

    double nextDouble() {
        return Double.parseDouble(next());
    }

    // 是否由下一个
    boolean hasNext() {
        while (st == null || !st.hasMoreTokens()) {
            try {
                String line = br.readLine();
                if (line == null)
                    return false;
                st = new StringTokenizer(line);
            } catch (IOException e) {
                throw new RuntimeException(e);
            }
        }
        return true;
    }
}

